This invention relates to the recovery of nickel and cobalt from aqueous ammoniacal solutions containing these metals.
Numerous nickel and cobalt-enriched ammoniacal solutions are known to those skilled in the art. For example, ammoniacal carbonate solutions containing nickel and cobalt are produced commercially by heating cobalt-containing nickeliferous ores in a furnace with a reductant gas and then leaching the reduced ores in the presence of oxygen with an aqueous solution of ammonium hydroxide and ammonium carbonate. As in known, the nickel and cobalt values in the ore dissolve in the solution as nickel-ammonia complexes and cobalt-ammonia complexes. Examples of the production of such ammoniacal carbonate solutions are described in detail in U.S. Pat. Nos. 1,487,145 and 3,100,700, and in "The Winning of Nickel", J. R. Boldt, Jr., Van Nostrand Co., Inc., Princeton, N.J. (1967), pp. 425-537.
Ammoniacal chloride solutions containing nickel and cobalt are prepared by leaching reduced lateritic ores with an aqueous leach liquor containing ammonium hydroxide and ammonium chloride. Ammoniacal chloride solutions are also prepared by dissolving or redissolving a nickel and cobalt containing material such as a nickel matte, a basic nickel carbonate, mixtures of nickel carbonates and cobalt carbonates, a nickel oxide, nickel scrap, a nickel alloy or mixtures of nickel sulfide and cobalt sulfide containing nickel and cobalt in varying proportions, in an aqueous solution of ammonium hydroxide and ammonium chloride, or in aqueous hydrochloric acid followed by adjustment of the solution pH to above 7 and normally above 8, with ammonia.
Ammoniacal sulfate solutions containing nickel and cobalt are prepared by leaching reduced lateritic ores with an aqueous leach liquor containing ammonium hydroxide and ammonium sulfate. Ammoniacal sulfate solutions are also prepared by dissolving or redissolving a nickel and cobalt-containing material such as a nickel matte, a basic nickel carbonate, mixtures of nickel carbonates and cobalt carbonates, a nickel oxide, a nickel alloy, nickel scrap, mixtures of nickel sulfide and cobalt sulfide containing nickel and cobalt in varying proportions, in an aqueous solution of ammonium hydroxide and ammonium sulfate, or in aqueous sulfuric acid followed by adjustment of the solution pH to above 7, and normally above 8, with ammonia.
As is known, the nickel and cobalt values dissolve in such ammoniacal solutions as nickel-ammonia complexes and cobalt-ammonia complexes.
Since it is commercially desirable to separate the cobalt from the nickel, numerous separation processes have been developed. In one known process, the ammoniacal solutions containing the cobalt and nickel are treated with a sulfiding agent, the objective being to selectively precipitate the cobalt as cobalt sulfide while leaving the nickel dissolved in the mother liquor. This separation technique is based upon the known principle that cobalt sulfide tends to precipitate in advance of the nickel sulfide under properly controlled sulfiding conditions. Unfortunately, however, substantial amounts of nickel sulfide ordinarily coprecipitate with the cobalt sulfide. This is undesirable because the proportion of cobalt in the precipitate is diminished thus making recovery of the cobalt more difficult. Moreover, the mother liquor, which is the source of recovered nickel values, has had its nickel content substantially diminished by the coprecipitation of nickel sulfide with the cobalt sulfide. It is apparent, therefore, that a method for retaining as much nickel as possible dissolved in the ammoniacal solution during sulfiding would be most desirable, as would a method for enriching the cobalt content of the sulfide precipitate.
It is an object of this invention, therefore, to provide a method for improving the selectivity of the separation of the cobalt from the nickel during the sulfiding of ammoniacal solutions containing dissolved nickel and cobalt.
It is another object of the invention to provide a method for separating cobalt from the nickel dissolved in an aqueous ammoniacal solution, using a sulfiding treatment, by which coprecipitation of nickel sulfide with the cobalt sulfide is minimized, thereby retaining more nickel in the mother liquor and producing a precipitate of enriched cobalt content.
It is another object of the invention to provide a method for increasing the amount of cobalt which precipitates during the selective sulfiding of aqueous ammoniacal solutions containing nickel and cobalt without simultaneously increasing the amount of nickel which coprecipitates with the cobalt.
It is a further object of the invention to provide a method for altering the chemical form of the nickel dissolved in aqueous ammoniacal solutions prior to selectively sulfiding such solutions, whereby more nickel remains in solution during sulfiding, and consequently less coprecipitates with the cobalt.
These and other objects of the invention will be apparent to those skilled in the art from a consideration of this entire specification.